Wide-band circulator

ABSTRACT

A wide-band circulator employing a Y-shaped stripline conductor having a generally circular center section and a plurality of symmetrically spaced, generally sector-shaped arms extending radially from the center section, in a preferred embodiment each sector-shaped arm subtending an angle 2 theta where theta can vary between 17.5* and 27.5*. The circulator futher includes a disk-shaped ferrite plate on each side of the stripline conductor and an outer conductor covering each ferrite plate.

United States Patent [191 Nishiyama Nov. 13, 1973 [73] Assignee:

WIDE-BAND CIRCULATOR Yutaka Nishiyama, Ichikawa, Japan TDK ElectronicsCompany, Limited, Tokyo, Japan Filed: Nov. 19, 1971 Appl. No.: 200,529

Related US. Application Data [63] Continuation-impart of Ser. No.17,528, March 9,

1970, abandoned.

inventor:

30 Foreign Application Priority Data Mar. 29, 1969 Japan 44/27590 [52]11.8. C1. 333/11, 333/34 [51] Int. Cl. H01p l/32, HOlp 5/12 [58] Fieldof Search 333/1.1

[56] References Cited UNITED STATES PATENTS 3,165,711 1/1965 Drumhelleret al 333/1-.1

Stelzer 333/l.l Andre 333/l.l

Primary Examiner-Paul L. Gensler Attorney-C. Frederick Leydig et a1.

[57] ABSTRACT A wide-band circulator employing a Y-shaped striplineconductor having a generally circular center section and a plurality ofsymmetrically spaced, generally sector-shaped arms extending radiallyfrom the center section, in a preferred embodiment each sectorshaped armsubtending an angle 20 where 0 can vary between 17.5 and 275. Thecirculator futher includes a disk-shaped ferrite plate on each side ofthe stripline conductor and an outer conductor covering each ferriteplate.

3 Claims, 5 Drawing Figures WIDE-BAND CIRCULATOR The present applicationis a continuation-in-part of Nishiyama application Ser. No. 17,528,filed Mar. 9, 1970, for Wide-Band Circulator, which is now abandoned.

Wide-band circulators are commonly used in microwave circuits for, as anexample, VHF and UHF operation. Though various types of circulators areavailable, such as wave guide circulators, coaxial circulators, lumpedelement circulators, and the like, it is highly desirable that allcirculators be operable over a wide frequency bandwidth at optimumoperating characteristics. Among the operating characteristics whichdetermine the optimum operation of a circulator are the insertion loss,the isolation, and the voltage standing wave ratio (V.S.W.R.).

It is an important object of this invention to provide an improvedwide-band circulator with a Y-shaped stripline having optimum operatingcharacteristics over a large frequency bandwidth.

A further object of the present invention is to provide a wide-bandcirculator which is operative over a large frequency bandwidth withparticularly improved forward and backard losses.

Other objects of the invention will become apparent upon reading theattached detailed description and upon reference to the drawings inwhich:

FIG. 1 is a wide-band circulator in a fragmented section employing thepresent invention;

FIG. 2 is a prior art center conductor for use in a conventionalcirculator;

FIG. 3 is a Y-shaped stripline, constructed according to the presentinvention for use as a center conductor in a wide-band circulator;

FIG. 4 is a graphic comparison of the operating characteristics of aconventional prior art circulator and of a wide-band circulatorconstructed according to the present invention; and

FIG. 5 is a graph showing the variation in the operative frequencybandwidth of a wide-band circulator constructed according to the presentinvention with variation in the shape of the Y-shaped stripline.

While the invention has been described in connection with certainpreferred embodiments, it will be understood that I do not intend to belimited to the particular embodiments shown but intend, on the contrary,to cover the various alternative and equivalent constructions includedwithin the spirit and scope of the appended claims.

Turning now to the construction shown in FIG. 1, the wide-bandcirculator includes two outer conductor plates 1 between which aresandwiched ferrite plates 2. A center conductor 3 is mounted between theferrite plates in a conventional manner. Exterior to the circulator aremagnets a and 10b which are effective to bias the circulator with a DC.magnetic field.

An example of a typical prior art center conductor 3 is illustrated inFIG. 2. In order to regulate the ratio between forward and backwardlosses, or insertion loss and isolation, the length L of the wings 4 andthe width W of the arms 5 on the prior art center conductor are variedto obtain a desired ratio. 7

The operating characteristics of circulators using such prior art centerconductors are illustrated in FIG. 4 by the solid-line curves 0, a, anda". An inspection of these three curves shows that the isolation curveis above 20 db, the V.S.W.R. curve is below 1.2 and the insertion losscurve is below.0.3 db, which are accepted limits on the optimumoperating characteristics of a circulator, for a bandwidth which is onlyapproximately 2 percent of the center frequency f,,. Outside of thissmall bandwidth the operating characteristics of the prior artcirculator of FIG. 2 are outside the limits of optimum operation. Thereare other prior art circulators which are operable within thesedesirable limits of the operating characteristics, but the maximumbandwidths for such optimum operation by these circulators do not exceed40 percent of their center frequencies.

Referring now to FIG. 3, there is illustrated a center conductor 3constructed in accordance with the teachings of the present invention toprovide a circulator which is operable within the above-noted operatingcharacteristic limits over a bandwidth which significantly exceeds 40percent of its center frequency. This center conductor or Y-shapedstripline 3 comprises a plate, preferably a copper plate, which has agenerally circular-shaped center section 6 and three generallysector-shaped arms 7, 8 and 9 which extend radially from and are locatedsymmetrically about the periphery of the circular center section. One ofthe ferrite disks 2 is shown positioned below the Y-shaped stripline asit would be in the wideband circulator. To operatively connect thestropline, and thus the circulator, to lead wires to the transmissionmedium, connectors X X and X are mounted respectively on the extremitiesof arms 7, 8 and 9.

This particular structure of the Y-shaped stripline results in improvedoperation of the circulator over a much wider bandwidth than ispresently attainable in prior art circulators using conventional centerconducturs. An important feature of the invention resides in the angletranscribed by the sector-shaped arms of the stripline; through largevariations in the angle 0, which is one-half the angle transcribed by asector-shaped arm, the circulator will operate within the limits ofoptimum operation and, in particular, will operate with isolation above20 db. Further it has been found that by setting 0 equal to 25 optimumoperation is obtained.

Using a center conductor constructed according to the present inventionhaving a circular center section with a diameter a= 5 mm andsector-shaped arms each with an angle 0= 25 and a length L'= 14mm andhaving a center frequency ft 3.5 GHZ, the curves b, b, and b" in FIG. 4-were derived indicating respectively the variation of isolation,insertion loss, and V.S.W.R. as the operating frequency varied. It canbe seen from these curves that the circulator functions within thelimits of optimum operation over a bandwidth of approximatelyl.7 GHZwhich is almost 50 percent of the center frequency. Referring to FIG. 5,the variation in the bandwidth within which the circulator constructedin accordance with the invention functions within the limits of optimumoperation as a function of 0, one-half the angle transcribed by eachsector shaped arm of the stripline, is shown with the bandwidthrepresented by its percentage of the center frequency. It is easilyappreciated that for l7.5 s 0 s 27.5 the present circulator operateswithin a bandwidth that exceeds 40 percent of the center frequency whichis the highest percentage attainable in known prior art circulators.

Thus, in accordance with the invention there has ally circular-shapedcenter section and a plurality been provided a wide-band circulator thatis operative of symmetrically spaced, sector-shaped arms exwithingenerally accepted limits of optimum operation tending radially fromsaid center section. within a bandwidth that approaches 50 percent ofthe 2. In a wide-band circulator adapted to be biased by centerfrequency of the circulator. 5 a magnetic field, the combination asdefined in claim I claim as my invention: 1 wherein 1. In a wide-bandcirculator adapted to be biased by each of said sector-shaped armssubtends an angle 26 a magnetic field, the combination comprising where0 is within a range of approximately 175 to two outer conductor plates;approximately 27.5.

two ferrite plates sandwiched between said outer 3. In a wide-bandcirculator adapted to be biased by conductor plates; and a magneticfield, the combination as defined in claim an inner conductor plate heldbetween said ferrite 2 wherein 0 equals 25.

plates, said inner conductor plate having a gener-

1. In a wide-band circulator adapted to be biased by a magnetic field,the combination comprising two outer conductor plates; two ferriteplates sandwiched between said outer conductor plates; and an innerconductor plate held between said ferrite plates, said inner conductorplate having a generally circular-shaped center section and a pluralityof symmetrically spaced, sector-shaped arms extending radially from saidcenter section.
 2. In a wide-band circulator adapted to be biased by amagnetic field, the combination as defined in claim 1 wherein each ofsaid sector-shaped arms subtends an angle 2 theta where theta is withina range of approximately 17.5* to approximately 27.5*.
 3. In a wide-bandcirculator adapted to be biased by a magnetic field, the combination asdefined in claim 2 wherein theta equals 25*.